In the field of custom printing of clothing, apparel or other objects, there are two prominent techniques of applying a print: digital printing and screen printing. The former typically requires less image processing and produces higher-quality prints, but is generally slower and more expensive in runs with many units. Screen printing is therefore the preferred option for high-volume production, especially when used to print non-photo-realistic images.
In screen printing, different colour printing inks are applied to a product substrate one at a time, in layers. This technique is illustrated using a two-colour palette of green and red in FIGS. 7, 8, and 9. FIG. 7 illustrates a resulting print of an image comprised of a tree printed completely in green, a house printed completely in red, and a bird printed by applying a combination of both red and green inks. FIG. 8 depicts the content of the separation plate used to apply green coloured ink for the example composite print of FIG. 7. FIG. 9 depicts the content of the separation plate used to apply red coloured ink to the substrate in the example composite print of FIG. 7. As shown in FIGS. 8 and 9, each colour plate is a black-and-white, grayscale image that defines where the corresponding ink (i.e. green or red, in our illustration) shall be applied onto the substrate and in what relative amount. This set of black-and-white images (often referred to as “plates”), together with their order of application to the product substrate are called a colour separation.
The number of inks that can be used in one screen-printing job is fairly limited, with the maximum typically ranging from 6 to 20 colours. This limitation comes from the historical economics of setup and the technical limitations of the machines used for the production.
Thus, traditional screen printing requires non-trivial pre-processing of the printed graphics that consists of selecting the inks that will be used to print the image and separating the image into layers, one for each ink. This pre-processing step is traditionally done by graphics professionals, requiring up to tens of hours of labor to produce acceptable colour separations to produce complex graphics. Even when this pre-processing step is performed with care, the output quality varies greatly, as the process leaves a non-negligible margin for error.
There are several common colour separation methods. These include, but are not limited to, index colour, spot colour, process colour and simulated process colour separations. Some of these methods can be used only on specific types of artwork; and some change the look of certain artwork more than others.
Process colour separations, for instance, use a CMYK approach that is typical for printing on paper. It uses four primary colours: cyan (C), magenta (M), yellow (Y), and black (K). This method, however, produces prints with a limited colour gamut, especially when used in association with dark fabrics.
When printing a more complex image (such as a photo), choosing a good palette becomes a difficult task. Generally, the more colours used in producing an image, the better the result. This improved result has traditionally come at a higher than desirable cost, for each colour used a separate costs is incurred, as more ink has to be prepared and additional screens need to be produced for the printing job.
Thus, it would be useful for the printing industry to have a system and method for quickly creating colour separations that together produce acceptable colour replication of an image for use in multi-stage printing processes. It would be additionally useful for the industry to have a system and method for simulating the results of a colour separation to facilitate an ability to evaluate a proposed colour separation without having to spend money on a bad design.